This invention pertains to methods and apparatus for thermally affecting tissue, and, more particularly, is directed to methods and apparatus for cooling brain tissue.
The medical profession has long known that the human brain is highly susceptible to injury following the reduction or cessation of blood flow thereto. Such injury often occurs, for example, following stroke, cardiac or respiratory arrest, or as a result of other bodily trauma. The medical profession also has long known that the application of cold to the human body slows the body's metabolic activity.
Based on this collective knowledge, plus the fact that brain injury usually has debilitating, irreversible consequences to a victim thereof, scientific research has focused upon inducing hypothermia to reduce the likelihood and/or extent of such brain injury.
Early research efforts (i.e., those prior to 1970) in this area focused upon global body hypothermia, in which a patient's entire body is cooled, e.g., to approximately 30-32° C., in order to concurrently cool brain tissue. In recent years, however, such techniques have been criticized by those in the art as tending to cause conditions (e.g., depression of systemic immune function, creation of cardiac arrhythmias, reduction of cardiac output) that can result in organ damage.
Consequently, more recent research in this art has focused upon achieving brain cooling through localized hypothermia. Among such research efforts are those described in U.S. Pat. Nos. 5,957,963, 5,916,242, 5,716,386, 5,531,776, and 5,474,533. Also in this vein are the approaches set forth in U.S. Pat. Nos. 3,897,790 and 3,776,241.
The U.S. Pat. No. 5,957,963 patent discloses a catheter that is placed within an artery that carries blood to the brain. Coolant is circulated into the catheter to cool the artery, thus cooling the blood flowing from the artery to the brain, and, in turn, cooling the brain itself.
The U.S. Pat. No. 5,916,242 patent discloses a collar that is worn around the neck to cool the carotid artery, thus cooling the brain via cooled blood flowing from the carotid artery to the brain. It also discloses the use of a tube that is inserted into a patient's trachea until it is in intimate contact with the back of a patient's oral cavity and, thus, in contact with blood vessels located thereat. Coolant is then flowed into the tube to cool the blood vessels, which carry cooled blood into the brain.
The U.S. Pat. Nos. 5,716,386, 5,531,776, and 5,474,533 patents are directed to devices that are positioned within the esophagus such that a heat transfer surface of the device is juxtaposed with a thoracic vessel. Coolant is then pumped through the device to cool the blood contained in the thoracic vessel, which, in turn, flows into and lowers the temperature of a patient's cerebellum.
The U.S. Pat. Nos. 3,897,790 and 3,776,241 patents disclose a technique for achieving brain cooling by locally irrigating the surface area of the nasal mucosa in order to cool the temperature of blood destined for the cavernous sinus which is in proximity to the brain.
Although such techniques are perhaps effective to manipulate brain temperature, they are likely highly inexact. This is because, for example, even after one ceases cooling one or more arteries or vessels using such techniques, the blood being carried to the brain via the vessel(s) or artery/arteries will continue to cool brain tissue for a residual time period until the blood returns to its normal temperature. Furthermore, by cooling specific vessels, one merely cools brain tissue closest to those vessels and their major arteries.
Therefore, a specific need exists for methods and apparatus that are capable of achieving safe, effective and precise localized brain cooling.
Moreover, a general need also exists for methods and apparatus that allow safe, effective and precise thermal affecting (i.e., temperature manipulation) of tissue.